Participants in this research study will consist of 2 groups. One group will have a moderately high blood cholesterol level. The purpose of this study is to provide a nutritional, non-drug therapy to lower blood cholesterol levels and reduce the risk for heart disease. A substance in plants called sitostanol has been shown to block the absorption of dietary cholesterol that leads to a lower blood cholesterol level. Several companies have developed sitostanol-containing products. They have put sitostanol into margarine for use in this study. Another food that has been shown to decrease the risk of heart disease is fish oil. Fish oil contains omega-3 fatty acids. These fatty acids lower the blood triglyceride level, decrease the formation of blood clots that can block an artery and cause a heart attack and keep the heart beating in a normal rhythm. This study will show if sitostanol and fish oil are a good combination therapy to decrease the risk of heart disease. The second group of participants in this research study include those with an inherited disorder, sitosterolemia. The purpose of this study is to provide a nutritional, non-drug therapy to lower blood cholesterol and sitosterol levels and reduce the risk for heart disease. A substance in plants called sitostanol has been shown to block the absorption of dietary cholesterol that leads to a lower blood cholesterol level. This study will determine if sitostanol will also lower the blood sitosterol level. Several companies have developed sitostanol-containing products. They have put sitostanol into margarine for use in this study.